The present invention relates generally to the field of telecommunications and, more specifically, to an architecture for connecting a plurality of programmable telecommunications switches to provide an expandable switching system and direct access for diverse communications applications.
A fundamental consideration in any telecommunications system design is switching capacity. Switching capacity must be analyzed in terms of current demand and projected demand in order to find a solution that is cost effective for both present and future service. For example, assume that a developing country is in the process of building a basic telecommunications system and intends to provide service to most of its current population. Such a population is most likely geographically distributed among small areas of high density (cities) and larger areas of low density (suburban and rural). In addition, the population is probably growing, but at different rates in different areas. Thus, the challenge for a telecommunications system designer is to provide sufficient switching capacity to support satisfactory service to most or all of the population while also anticipating likely increases in future demand and providing for economical expansion.
Another example of the difficulty of providing appropriate switching capacity involves wireless or personal communications network (PCN) applications. These types of applications are based on micro-cellular architectures which require numerous base-stations, in close physical proximity across a metropolitan area, with different switching capacities which aggregate to a large capacity.
A second fundamental consideration in telecommunications system design is providing for the addition of new features or services in the future. Telecommunications equipment and service continues to evolve rapidly, due in large part to the advent of digital technology. Even more dramatic advances are likely in the future, particularly as previously separate industries such as cable television and local telephone operating companies integrate their services. Again, the challenge is to create a system which economically serves a present need, while also providing flexible and inexpensive ways to integrate new features and services as they become available.
Of the conventional approaches to the dual problems of providing adequate switching capacity along with access for new features and services, most, if not all, suffer from one or both of two major disadvantages: (1) there is insufficient bandwidth in the system to handle information such as video or multimedia (in addition to voice and data), (2) there is no direct, ready access to all of the information passing to or from the system, meaning there is no way to capture all of the information and distribute it to other switching systems or equipment, and (3) an increasingly large central switch is required to provide access to some types of enhanced services.
One conventional approach may be referred to, for shorthand, as the xe2x80x9cbus extensionxe2x80x9d approach. In many conventional telecommunications switches, one or more internal buses are provided for carrying information, including voice, data and control information, between various parts of the switch. Buses are well suited for carrying such information since, by definition, multiple devices (e.g., circuit boards or cards) may interface with the buses and share them in accordance with a defined communication protocol. In a telecommunications switch, it is typical to find one or more buses interconnecting a series of cards which physically terminate telephone lines or trunks with other cards which perform switching, control or other functions.
As the shorthand name suggests, the concept underlying the bus extension approach is simply to connect additional cards, which provide additional switching capacity or other functions, with the existing buses. In addition to the two major disadvantages noted above, there are several other disadvantages to this approach. First, there are physical limitations as to the number of cards that can be physically connected to or share the buses without degrading the system""s performance. Second, in order to permit significant future expansion, the buses and other portions of the system must be constructed, in the first instance, to handle far greater traffic than is required prior to any expansion of the system. These limitations are related to the electrical and mechanical characteristics of the buses (or perhaps a particular one of the buses) and their effective operating speeds. Attempts to overcome these limitations (e.g., using an excessively large number of connections to the bus) tends to increase the cost and complexity of the xe2x80x9cbasexe2x80x9d or unexpanded system, possibly rendering the system too costly for some applications. There is also a limitation related to the processing power required to actually performing the switching functions as well as control traffic on the buses.
Third, the bus structures found in many, if not most, conventional switching systems are generally designed solely for carrying out basic call processing and switching functions and do not provide ready, direct access to the ports for integrating new features and services.
Fourth, the bus structures are typically incapable of carrying packet switched data or other types of information.
A second approach may be referred to as the xe2x80x9cmodularxe2x80x9d approach for shorthand. In the modular approach, the concept is to provide a switching system which is constructed from a series of essentially identical modules. Each module provides a finite amount of switching capacity which may be added to an existing system (one or more at a time) to increase the overall capacity of the system.
Again, in addition to the major disadvantages noted earlier, the modular approach has other deficiencies. In order to provide fully non-blocking operation, each and every module as built must have the capability to receive circuit switched data from every other module up to whatever the maximum number of modules may be. In terms of hardware, this means that each module must be built with a sufficiently large memory to hold the maximum amount of circuit switched data which could be received if the maximum number of modules are connected together. For example, if each module is capable of switching the equivalent of 64 ports and a maximum of eight modules may be connected together, then each module must necessarily contain a memory capable of holding circuit switched data for (8xc3x9764)=512 ports. Thus, in the modular approach, it is the maximum switching capacity of the fully expanded system which determines the size of the memory that each module must have. For larger systems (i.e., on the order of a few thousand ports or larger), constructing such a memory becomes impractical due to both the accompanying number of physical network/line interfaces as well as the additional circuitry needed to control the memory.
Second, in order to maintain a truly xe2x80x9cmodularxe2x80x9d system, it is impossible to vary the switching capacity of individual modules.
Third, like the bus extension approach, the modular approach is oriented toward performing basic switching operations and does not generally offer direct access to all the ports nor the capability of handling packet switched data or other types of information.
In brief summary, the present invention provides an open, high speed, high bandwidth digital communication network for connecting multiple programmable telecommunications switches to form a large capacity, non-blocking switching system. In a preferred embodiment, the network is implemented using one or more rings which provide a medium for transferring information over the network, and a plurality of programmable switches, each of which appears as a node on the network and serves a group of ports. Additional switches (nodes) may be added to the network as desired to increase the system""s switching capacity.
Each node includes circuitry for transmitting and receiving variable-length, packetized information over the network, thus enabling each node to receive information from or transmit information to all other nodes. The network may carry any type of information present in the system including voice, data, video, multimedia, control, configuration and maintenance, and the bandwidth of the network may be divided or shared across various information types.
In addition, devices or resources other than programmable switches may also act as nodes on the network, thereby gaining direct access to all information passing through the network. More specifically, voice processing resources such as voice mail/message systems or other enhanced services platforms may, by becoming nodes, gain direct access to all ports served by the system without the need for a large central switch. The present invention""s ability to transfer information of any type, in a readily usable form, at high speed across the network enables any service, feature or voice processing resource which is available at a given node to be provided to any port of the same or any other node.
The present invention also provides methods and packet structures for communicating information over the network. In general, different packet structures are provided for communicating circuit switched information, voice processing information, data or maintenance information. However, all packets contain a control portion or header, which typically includes address, status and other control information, and a payload portion for carrying data. The combination of direct access to all ports and the ability to transfer information in packet form is highly compatible with asynchronous transfer mode (ATM) operation on SONET networks.
In accordance with one method of transferring information between nodes, each node uses the network to transmit one or more packets, each of which has an xe2x80x9cemptyxe2x80x9d payload, which are received first by an adjacent node. The adjacent node determines the source of the received packet and the packet""s status by the information contained in the control portion of the packet. If that adjacent node has information to send to the node which transmitted the packet, the adjacent node inserts such information into the payload of the packet, then allows the packet to pass to the next adjacent node on the network. If the adjacent node has no information for the node that originated the packet, the packet simply passes to the next adjacent node on the network. This process is repeated at each node until the packet traverses the complete network and returns with a xe2x80x9cfullxe2x80x9d payload to the node from which it originated. At that point, information which was inserted into the packet by other nodes is captured by the node which originated the packet. In turn, each node transmits an xe2x80x9cemptyxe2x80x9d packet which traverses the network and returns with information from other nodes. In this fashion, information of any type originating from any port served by any node may be transferred to any other port of the same or different node in the system.
In accordance with an alternative method of transferring information between nodes, each node uses the network to transmit one or more packets, each of which has a xe2x80x9cfullxe2x80x9d payload that contains information originating from that node. Each such packet is initially received by an adjacent node which determines the origin of the packet and whether any of the information contained therein is needed by that adjacent node. If so, such information is captured from the payload before the packet passes to the next adjacent node. If no information is needed, the packet simply passes to the next adjacent node. Again, this process is repeated until each node on the network has transmitted one or more packets with a xe2x80x9cfullxe2x80x9d payload and each such packet has traversed the complete network, thereby allowing each node access to the information originated by each other node.
By operating in accordance with either (or both) of the inventive methods of transferring information, the capacity of each node to transfer information over the network may be advantageously established independently from the other nodes. Further, a given node need only contain a memory which is sufficiently large to accommodate that node""s switching (or voice processing) capacity and not the entire capacity of the system.
In another embodiment of the present invention, a second ring is used to connect all of the nodes, thereby providing a second network. The second network effectively doubles the maximum switching capacity of the system and also provides fault isolation in the event of a failure of the first network or one of the nodes.
In another embodiment of the present invention, one or more additional networks are added to the nodes, further increasing the maximum switching capacity of the system and providing redundancy.
In yet another embodiment of the present invention, one or more nodes may be used to xe2x80x9cbridgexe2x80x9d one network to another. A bridge node is common to two networks and is capable of exchanging information bidirectionally between such networks. A bridge node may also be used to connect networks which operate at different speeds.